The crystalline lens of a human's eye refracts and focuses light onto the retina. Normally the lens is clear, but it can become opaque (i.e., when developing a cataract) due to aging, trauma, inflammation, metabolic or nutritional disorders, or radiation. While some lens opacities are small and require no treatment, others may be large enough to block significant fractions of light and obstruct vision.
Conventionally, treatments to the cataract involve surgically removing the opaque lens matrix from the lens capsule using, for example, phacoemulsification and/or a femtosecond laser through a small incision in the periphery of the patient's cornea. An artificial intraocular lens (IOL) can then be implanted in a lens capsule bag (the so-called “in-the-bag implantation”) to replace the crystalline lens. Generally, IOLs are made of a foldable material, such as silicone or acrylics, for minimizing the incision size and required stitches and, as a result, the patient's recovery time. The most commonly used IOLs are single-element lenses (or monofocal IOLs) that provide a single focal distance; the selected focal length typically affords fairly good distance vision. However, because the focal distance is not adjustable following implantation of the IOL, patients implanted with monofocal IOLs can no longer focus on objects at a close distance (e.g., less than twenty-five centimeters); this results in poor visual acuity at close distances. To negate this disadvantage, multifocal IOLs are used to provide dual foci at both near and far distances. However, due to the optical design of such lenses, patients implanted with multifocal IOLs suffer from a loss of vision sharpness (e.g., blurred vision). In addition, patients may experience visual disturbances, such as halos or glare, because of the simultaneous focus at two distances.
Recently, accommodating intraocular lenses (AIOLs) have been developed to provide adjustable focal distances (or accommodations) relying on the natural focusing ability of the eye (e.g., using contractions of ciliary muscles). Conventional AIOLs include, for example, a single optic that translates its position along the visual axis of the eye, dual optics that change the distance between two lenses, and curvature-changing lenses that change their curvatures to adjust the focus power. These designs, however, tend to be too complex to be practical to construct and/or have achieved limited success (e.g., providing a focusing power of only 1-2 diopters).
Additionally, IOL implantations may cause post-surgical complications. For example, when the crystalline lens is removed through a small incision in the anterior part of the lens capsule, the posterior side of the capsule is left intact to prevent vitreous humor from entering the anterior chamber of the eye. The intact posterior lens capsules, however, may develop haziness of the capsule, known as posterior capsular opacification (PCO), which results in blurry vision. This is due to the growth and migration of lens epithelial cells on the lens capsule, which frequently remain present following cataract surgery and represent one of the most common post-surgical complications of IOL implantation. Although a neodymium-doped yttrium aluminium garnet (Nd:YAG) laser may be utilized to open an aperture in the posterior lens capsule to remove the opacity of the capsule, and thereby restore vision, this treatment requires an extra procedure and poses an additional risk of damaging the implanted IOLs.
Consequently, there is a need for IOLs that provide a high degree of accommodation and appropriate focusing power, and which can be easily manufactured and implanted in human eyes. In addition, it is desirable for surgical complications, such as PCO, to be avoided after IOL implantation.